Moving-coil electrical instrument



June 15 {1926.

' w. s. PuRsER MOVING COIL ELECTRICAL INSTRUMENT Filed Feb. 11, 1926 Patented dune 15, 1926.

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WILLIAM SPENCER PURSER, 0F PALMERS GREEN, LONDON,- ENGLAND; ASSIGNOR Ti COLUMBIA GBAI'HOPHON'E COMPANY, LIMITED, OF LONDON, ENGLAND.

MOVING-COIL ELECTRICAL INSTRUMENT.

Application filed February 11, 1926,

This invention relates to sound recorders, sound amplifying devices or loud speakers and microphones ot' the'ltind involving a moving coil. system.

The. object of the present invention is to devise improvements in the construction and arrangenn-mt ot apparatus of the above character which 'will increase their sensitivity. and the invention consists in sound recorders. sound-amplitying devices and micro-' phones of t"e kind reterred to embodying a plane or tiat coil which may be mounted between two adjacent plane or flat parallel magnet poll. pieces so that he plane of the coil is parallel to the faces of said pole pieces.

The invention also consists in apparatus of the above character in which the coil is formed as a tlat spiral.

The invention further consists inapparatus oi the above character in which suhe stant'ially only one-halt the coil is situated in the magnetic field.

The invention also consists in the apparatus hereimtl'ter described or indicated.

The accompanying drawings illustrate teo modes of carrying out the invention.

Figure l is an elevation of one term of apparatus in accordance with the invention;

Figure 2 is a side elevation, and

Figure 3 is an underneath plan of a part of the apparatus shown iii-Figure l Figure 4 is a pers 'iective view of a modified form of apparatus in accordance with the invention;

Figure 5 is an elevation of the coil shown in Figure. 4. and

Figure 6 is a. view showing the invention applied to a microphone.

In carrying my invention into effect in one convenient manne" as, for example, in its application to a sound-amplifying device or soealled loud speaker as employed in (Ol'llltttlfln with wireless telephony. and as illustrated in Figures 1 to 3, I attach to the dia 'ihragm a of the loud speaker a tlat coil I) in the term of a flat spiral. the coil. which .carries the incoming telephone currents, being mounted at right angles to the diaphragm and to the magnetic field produced by the electromagnet c of the loud speaker nd being tree to move in and out between he pole pieces of such electroniagnet.

The magnet poles a} are rectangular in Serial No. 87,727, and in Great Britain December 16, 1924. v i

shape with or without rounded edges and are separated by a distance which is just sufiicient to allow the fiat coil to'clea-r each of the adjacent, flat parallel pole faces, the advantage of such an arrangement being that it is possible to considerably reduce the total space between the poles, thus increasing the strength of the magnetic field and the sensi tivity of the instrument. Another advantage of the small gap is that the spaces may be tilled with sponge rubber or with oil or other liquid which, owing to the small di-- meusions of the gap, will be held in place by capillary attraction without the necessity for any container. Moreover, the air gap may be readily adjusted if desired.

()nedialtof the flat coil is situated within the magnetic field.

'lhe fiat thin spiral constituting the layer of the coil may consist oi fine insulated wire which may comprise any number of turns from the center to the outside edge, the numher ofturns and diameter ot the wire used being deterniinezt by the area of the pole pieces and the electrical or other characteristics of the instruments to which the invention is applied. r

The spiral may have retaining sides of mica or other thin rigid substanceand the whole be impregnated with parafiin wax or insulating varnish, or the cell may be impregnated with some substance to give it rigidity and be used Without retaining sides or other support for the wires.

A further method according to the invention is shown in Figures 4 and Where the coil is wound as a single twisted spiral, shaped somewhat as the figure 8, each flattened end being placed in a magnetic field while the central portion may be used as the means of suspension or point of attachment to its instrument.

The invention may similarly be applied to electrical sound recording devices and to microphones.

Figure 6 shows the application of the invention to a microphone, the arrangei'nent being similar to that. shown in Figure l with the exception that the 'diaphragn'i (L IS omitted and a pad or mounting a. of sponge rubber or the like provided for the support of the coil. In this modification a diaphragm need not be employed and is omitted as shown in the drawing.

:iezwmg new descri be invention what I claimfiis new a'n. desim t0 scure by Letters Patent; is:-

'1. In a taliewhenic instrument, a pair 0f 5 magnabpoles placed close together, a sub 'i-itantialiyrigid plane coil between said poles, coil having its plane substantially perpendicular to the field said poles, a116,

a. resiiiem'i "support far Saicl 001%, said; mil

Ewing miapted to am di'i'eetiy in time eiecimaccoustiq transfer of energy.

.2. In a telephonic instrument, a pair of magne'a psies'piaced cl'o's-e together, a subsmntiali ri id coil between said. 0125 :mci v a block of soft rubber supporting said. 00H. In testlmqny whereef i have signed my name is this SpeclfififitlOlL WILLIAM SPENCER PUB-SEE. 

